As more lawsuits claiming a link between Roundup and cancer move forward, a new report claims the main ingredient found in the weed killer is showing up in organic beer and wine.

U.S. PIRG tested samples of popular beer and wine brands and found the chemical, called glyphosate, in 19 out of 20 brands. Glyphosate is the main ingredient in Roundup, produced by agrochemical giant Monsanto. Sutter Home Merlot had the highest level of the weed killer of all 20 brands, at 51 parts per billion (ppb). Beringer Estates Moscato and Barefoot Cabernet Sauvignon had slightly smaller quantities of the chemical.

Tsingtao beer contained 49 parts per billion of the chemical. Corona, Miller Lite and Budweiser had between 25 and 30 ppb of the substance; Guinness and Heineken contained about 20 ppb. Beverages from Stella Artois and Sam Adams had trace amounts of the weed killer.

These levels are far below those that could potentially cause harm in humans, but suggest a troubling prevalence of the weed killer in nature, Kara Cook-Schultz, U.S. PIRG's toxics program director, told CBS News.

"If we're finding this level of glyphosate in wine and beer, even when we know the makers aren't using glyphosate, that to me indicates there's glyphosate in a lot of other products," Cook-Schultz said.

Peak Beer was the only tested brand that showed no levels of the chemical.

Cancer link disputed

Monsanto's parent company Bayer disputes that glyphosate causes cancer and called the PIRG report "misleading."

"The reality is that regulatory authorities have strict rules when it comes to pesticide residues," Bayer toxicologist William Reeves said via a spokesperson. "The U.S. Environmental Protection Agency sets daily exposure limits at least 100 times below levels shown to have no negative effect in safety studies."

The statement continued: "Assuming the greatest value reported, 51.4 ppb, is correct, a 125-pound adult would have to consume 308 gallons of wine per day, every day for life to reach the US Environmental Protection Agency's glyphosate exposure limit for humans. To put 308 gallons into context, that would be more than a bottle of wine every minute, for life, without sleeping."

Organic brands also affected

PIRG's investigation also found traces of the weed killer in some organic brands, which are forbidden from using most chemicals in food production. That doesn't mean these producers were circumventing the rules, but rather that glyphosate is so prevalent in the environment it can be hard to avoid, Cook-Schultz said.

"[At] the levels we found, I suspect they're not using glyphosate," she said of the organic producers, noting that the chemical could be carried to organic fields by irrigation water or could be present in the soil.

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The Environmental Protection Agency does not test for glyphosate in processed foods. But in recent years, tests by nonprofits and advocacy groups have found the chemical in cereals, snack bars and some Ben & Jerry's ice cream.

First developed by Monsanto (which merged with German pharmaceutical company Bayer last year) in the 1970s, Roundup has been the most widely used herbicide in the U.S. for nearly 20 years.

How much is too much?

California regulators have called glyphosate a "probable carcinogen," and France banned a version of Roundup last month due to health concerns.

How much glyphosate is safe to ingest is a matter of debate. The levels of the chemicals PIRG found are below what the state of California considers an acceptable level to consume, which is about 160 parts per million.

Monsanto maintains that glyphosate is safe. It will be defending that position in a lawsuit brought by a 70-year-old man alleges that the herbicide led to his cancer diagnosis in 2015.